Tantalum powder

ABSTRACT

AN IN SITU PRODUCED ELEMENTAL REFRACTORY METAL POWDER OF COHERENT SPONGE FORM CONSISTING ESSENTIALLY OF INTERCONNECTED PARTICLES EXHIBITING NECKING PROPERTIES WHEREIN A MAJORITY OF THE PARTICLES ARE LARGER THAN ONE MICRON IN SIZE AND THE MAJOR PORTION OF THE INDIVIDUAL PARTICLES HAVE SMOOTH, VERMICULAR CONFIGURATIONS AS OPPOSED TO SHARP, ANGULAR PLATE-LIKE SHAPES.

TANTALUM POWDER 2 Sheets-Sheet 1 Filed March 18, 1971 mm a July 24, 1973 DAVIS ET AL TANTALUM POWDER 2 Sheets-Sheet 2 Filed March 18, 1971 United States Patent O 3,748,106 TANTALUM POWDER Robert D. Davis, Newport Beach, Theodore N. Meyer, Westminster, and Roy L. Blizzard, Huntington Beach, Caliii, assignors to Plasmachem, Inc., Newport Beach,

Calif.

Filed Mar. 18, 1971, Ser. No. 125,529 Int. Cl. (32% 51/00; B221? 5/00 US. Cl. 29-192 9 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATION This application is related to the application of the inventors entitled Method and Apparatus for Production of Metallic Powders executed Mar. 9, 1971 and filed concurrently herewith and given Ser. No. 125,589 and a filing date of Mar. 18, 1971 and the substance of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION This invention pertains to a refractory metal powder such as tantalum, which is of unique configuration formed as an in situ product in a plasma reactor wherein the recovered tantalum is of exceptionally high purity, and which is obtained in copious amounts.

The use of refractory metals and in particular tantalum, has become increasingly important as technology has developed requiring metals which can resist exceptionally high temperatures. Moreover, the metal powders, such as tantalum, have other uses in the electronics field as for example, the fabrication of electrodes used in capacitors.

However, in capacitor usage, it is necessary that the tantalum powder have certain surface characteristics and be of a relatively pure nature so as to perform in an acceptable manner. The difiiculty in obtaining capacitor grade tantalum is well known in the art, and various techniques have been used to obtain tantalum powder of acceptable grade and quality.

Prior art tantalum powders have been of the crystalline or cubic form differing substantially from the tantalum of this invention.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to provide a tantalum powder of unique configuration.

It is another object of the invention to provide a tantalum powder having specific surface configuration of particular micron size.

It is still a further object of the invention to provide the tantalum powder recovered in a plasma reactor as a coherent sponge mass of interconnected particles.

It is still a further and more important object of the invention to provide a tantalum powder of high purity and exhibiting surface characteristics for obtaining desirable results in capacitor usage.

It is still a further and more specific object of the invention to provide an in situ produced elemental refractory metal of coherent sponge form consisting essentially of interconnected particles of the metal exhibiting necking properties.

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It is still another important and further object of the invention to provide a tantalum powder which is obtained in metallic sponge form in a plasma reactor process of the reduction of tantalum pentachloride.

Other objects and advantages of the invention will be apparent from the following specification and the accompanying drawings, which are for the purposes of illustration only.

Basically, in the exemplary form, the invention pertains to an in situ produced elemental refractory metal of coherent sponge form consisting essentially of interconnected particles of the metal exhibiting necking properties wherein a majority of the particles are larger than one micron in size and the majority of the individual particles have smooth, vermicular configurations as opposed to sharp, angular ones.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-4 inclusive are photomicrographs at various magnifications illustrating the tantalum powder of this invention; and

FIGS. 58 inclusive are comparative photomicrographs of prior art tantalum at corresponding powers of magnification for purposes of distinguishing the tantalum of the invention from the prior art.

DESCRIPTION OF THE BEST EMBODIMENTS CONTEMPLATED Generally speaking, as disclosed in the atorecited copending application of the inventors, an apparatus utilizing a plasma reactor of conventional design is modified to the extent that a collection zone is formed meeting the criteria as set forth in said application.

Sufiice to say that a plurality of runs were made wherein a feed material comprising tantalum pentachloride was injected into the reaction zone of the plasma reactor and reduced with hydrogen gas to thereby produce elemental tantalum which is recovered in the collection zone on a unique collection member as a metallic sponge cylinder approximately 15 centimeters in diameter, 2 centimeters thick and having various lengths depending on the collection apparatus and the length of individual production runs.

The tantalum powders of this invention are prepared by chemically reducing tantalum compounds such as tantalum pentachloride under chemically reactive conditions with a reducing agent, as for example, hydrogen. The passage of the products of reaction into a collection zone permits recovery of tantalum powder in a particular form wherein individual particles have selected surface characteristics and are of a particular size, the majority of which are over one micron.

The resulting tantalum sponge may be processed and utilized in various applications wherein tantalum is desired. For example, the recovered tantalum sponge may be mechanically broken up to provide tantalum powder of a specific form which may be fabricated into electrodes for use in capacitors.

-As disclosed in said aforecited. pending application, a plasma generator capable of generating reaction temperatures in the 2000 K. to 5000 K. range, was fabricated and a gas such as hydrogen used as the stabilizer gas to generate the plasma reaction zone. Into the plasma reaction zone is fed a feed material With or without a feeder gas comprising tantalum pentachloride. An excess of hydrogen is made available so as to permit substantially complete reduction of the tantalum pentachloride.

The products of reaction from the reaction zone are selectively passed into a collection zone wherein elemental tantalum is formed as the in situ product of the reduction process. The tantalum, as indicated earlier, forms as a coherent metallic sponge mass somewhat donut or cylindrical in shape depending upon the configuration of the collection member utilized in the collection zone. The ultimate size of the coherent mass also is dependent upon the length of the production run. The tantalum is recovered at particularly high purity levels with overall yields in excess of 90%, wherein the surface configuration of the formed tantalum differs substantially from that tantalum known in the prior art.

A series of experimental runs was conducted utilizing the apparatus disclosed in the aforecited application, wherein tantalum pentachloride using argon as a carrier gas was introduced into the plasma reaction chamber of a plasma generator. The stabilizer gas was hydrogen and the temperature within the reaction chamber was calculated to be within the range of about l800-2850 K. From the collection zone there was recovered a metal sponge mass which upon experimental analysis, was found to be tantalum.

The in situ formed elemental metal sponge was found to have individual particles exhibiting a necking property to produce interconnected particles forming a porous structure which upon grinding and sieving produced elemental particles or powder of the 1 to 10 micron size determined by gas permability using a Fischer Sub Sieve technique. The configuration of the metallic sponge is ascertainable by means of photomicrographs particularly FIGS. 1-4 inclusive.

FIG. 1 (all of the photomicrographs were taken at a voltage level of 10 kv.) depicts the formed metallic sponge at a magnification factor of ,1000. The porous nature of the in situ formed tantalum is fairly apparent.

FIG. 2, which is a photomicrograph at 5000 magnification begins to discernibly illustrate the vermicular shape of the formed tantalum.

FIGS. 3 and 4, which are at magnification levels of 10,000 and 20,000 respectively, clearly show that the formed tantalum consists essentially of interconnected particles of the metal wherein necking properties are exhibited and the overall configuration is such as to provide a smooth, vermicular character as opposed to that normally associated with prior art tantalum powder.

Referring now to FIGS. 5-8 inclusive, an agglomerated tantalum commercially available from Fansteel, Inc. and designated as their grade FD-30 type is shown. The difference between the prior art tantalum and the tantalum of this invention is abundantly clear.

FIGS. 5-8 inclusive correspond to FIGS. 1-4 respectively, and are photomicrographs at the same power level and at powers of magnification directly correlative to the photomicrographs of FIGS. 14.

Thus, the sharp, angular, plate-like configuration of the prior art tantalum is clearly seen and which configuration is totally different from the tantalum of this invention.

The tantalum was produced using the apparatus and method of the aforecited patent application, and tantalum recovered with a particle size as illustrated in the following table:

TABLE L- -FISCHER SUB SIEVE (ANALYSIS) Runs J&K (200 mesh) 4 Run M (-200 mesh) Porosity setting: Microns .80 1.15 .75 1.25 .70 1.55 .65 1.51 .62 1.65

Run M (+200 mesh) Run N (+200-- 100 mesh) Run M (+200-200 50/50) Run N (200 mesh) Run N (+200-200 50/50) Tantalum powder produced according to one of these runs was subjected to analysis to determine the purity thereof. Results of the analysis is accurately depicted in Table II below in parts per million.

Tests were conducted of the electrical properties of capacitor anodes made from the tantalum powder and produced from one of the foregoing runs. A commonly accepted criterion of the quality of capacitor anodes is the product of the capacitance and test voltage per unit weight of anode material. The tests indicate that the CV product per gram is comparable to powders in commercial usage.

Anodes sintered at 1900 C. gave CV/g. values in the approximate range of 2900-8360 and with a 2000 C. sinter, a value of 2400-2600 CV/ g. At a sintering temperature of about 1800 C., CV/g. values of approximately 4000-5100 were found.

The DC leakage current was one-quarter to one-half microampere in anodes sintcred at 2000 C.

Thus, not only does the tantalum of this invention possess unique physical attributes, but it is also useful for refractory metal powder use, such as in capacitors and is recovered in exceptionally pure forms without the necessity of employing prior art purification procedures, which are costly.

Obviously, other uses for the tantalum of this invention will present themselves to one of ordinary skill in the art and such variations and modifications are intended to be covered by the appended claims.

We claim:

1. An in situ produced elemental refractory metal of coherent sponge form consisting essentially of interconnected particles of the metal exhibiting necking properties and a majority of said particles being larger than one micron in size with the major portion of said individual particles having smooth, convuloted or vermicular configurations as depicted in FIG. 1 through FIG. 4, inclusive, as opposed to sharp, angular configurations.

2. The metal of claim 1 wherein said interconnected particles are vermicular in shape.

3. The metal of claim 2 obtained by the reduction of a refractor metal chloride.

4. The metal of claim 3 wherein said refractory metal chloride is tantalum pentachloride.

5. The metal of claim 4 wherein said reduction is carried out in a plasma-jet reactor.

6. The metal of claim 5 wherein said sponge is annularlike in shape.

7. The metal of claim 6 wherein said metal sponge is relatively free of contaminants.

8. The metal of claim 7 formed into an anode for capacitor usage.

9. The product of claim 1 wherein the metal is tantalum.

References Cited UNITED STATES PATENTS 3,473,915 10/1969 Pierret -05 B B 3,144,328 8/1964 Doty 75-84 3,158,671 11/1964 Socci 75--84.5 3,211,548 10/1965 Scheller et al 750.5 B B 3,464,813 9/1969 Shelton et al. 7584.4 3,480,426 11/1969 Nevenschwander 75--0.5 B B WAYLAND W. STALLARD, Primary Examiner US. Cl. X.R. 

